A hot asphalt mixture is usually used under an initial compacting temperature within a range of 110-140° C., such as provided by Pavement Construction Handbook (“Hosou Sekou Binran” in Japanese). However, even though the hot asphalt mixture can have a large strength immediately after being paved, the available period of time is until the temperature of the mixture decreases. Therefore, the application of the hot asphalt mixture may be difficult under various conditions, such as when a small amount of the mixture is divided to be used several times, when the mixture is transported for a long period of time, and when the constructed thickness is thin, such as in a thin layer overlay method, and the temperature significantly decreases immediately after the mixture is spread.
Accordingly, a hot asphalt mixture that uses a warm-mix technique and an ordinary temperature construction-type asphalt mixture are focused. The hot asphalt mixture that uses a warm-mix technique, i.e. a warm-mix asphalt mixture, is generally said to be able to extend the available temperature range of the hot asphalt mixture toward the lower limit side by about 30° C. The ordinary temperature construction-type asphalt mixture is an asphalt mixture that is said to allow the pavement construction under ordinary temperatures (100° C. or lower).
As an asphalt mixture that can be constructed under ordinary temperatures or under temperatures within a warm temperature region, for example, a so-called cutback asphalt mixture is proposed in which the viscosity of the asphalt mixture is forcibly reduced using a mineral oil or the like. In the cutback asphalt mixture, as disclosed in JP11-12475A, the asphalt is softened using a cutback material such as a mineral oil, and the strength of the asphalt mixture is developed as the cutback material is volatilized. However, according to the method in which, as described above, the asphalt is “cut back” using a mineral oil or the like thereby to forcibly reduce the viscosity at the time of pavement construction, there are drawbacks in that the mixture strength when the traffic of a road is opened, for example, may considerably deteriorate and the curing may require a long time.
An ordinary temperature construction-type asphalt mixture using an asphalt emulsion is also proposed, but the mixture has a relatively low strength even though the aggregate is not required to be heated and dried, and the applicable field may be limited because the decomposition rate of the asphalt emulsion may have to be taken into consideration. In addition, in the ordinary temperature asphalt mixture using an asphalt emulsion, the asphalt emulsion may possibly flow out if it rains before the emulsion is decomposed after the pavement construction.
In such a situation, JP Patent No. 5583978 discloses an ordinary temperature construction-type asphalt mixture that can be constructed under ordinary temperatures. This asphalt mixture uses a tall oil fatty acid as the cutback material (see, for example, “Naval Stores -Production- -Chemistry- -Utilization-” (published by Harima Chemicals Group, Inc., June 1993), line 10 of page 474 to line 9 of page 475). The tall oil fatty acid acts to reduce the viscosity of the asphalt mixture thereby to allow the pavement construction under ordinary temperatures. According to this technique of JP Patent No. 5583978, the tall oil fatty acid as the cutback material reacts with the cement after the pavement construction so as to act as a curing agent, which can thereby develop a sufficient strength.
On the other hand, also in an asphalt mixture that can be constructed under ordinary temperatures or under temperatures within a warm temperature region, the pavement body after the construction is required to have improved characteristics, such as further enhanced strength, durability, and flexibility. Therefore, an asphalt mixture is desired which can improve these characteristics and which can be constructed under ordinary temperatures or under temperatures within a warm temperature region.